Containers are manufactured in large quantities for a variety of purposes, including the containment of pressurized aerosols and beverages (e.g., soda, carbonated water, and beer). Such containers are generally made as thin as possible and with a configuration (e.g., necked-in ends) to minimize raw material (e.g., metal alloy) usage because even a small reduction in container thickness or change in shape can result in a substantial reduction in material costs for the manufacturer. In this regard, however, it is important that the required strength and other performance parameters of a container not be compromised by designs and manufacturing operations that reduce material usage.
Typically, beverage containers are manufactured from thin sheets of metal alloy that are subjected to a series of drawing, ironing, and forming operations. Initially, a metal sheet may be drawn into a seamless cup (e.g., a container with an open top portion, an outer wall, and a bottom portion) to establish an initial shape and inside diameter of the container. Subsequently, the container may be pushed through a series of ironing rings to thin the outer wall of the container to a selected thickness. During these ironing processes, the diameter of the container is typically maintained while the outer wall length is substantially increased to establish the fluid capacity of the container. The bottom portion of the container generally is formed to define a recessed or concave dome surface to resist deformation (e.g., due to internal fluid pressures). The pressure at which the recessed surface is deformed or reversed (e.g., pushed outward) is often called the static dome reversal pressure of the container. The bottom portion of the container also includes an annular support which will contact a supporting surface to maintain the container in a vertical position during stacking, consumer use, and the like. Finally, the bottom portion of the container generally contains outer and inner surfaces that join the outer wall to the annular support portion and that join the annular support portion to the domed surface, respectively.
The configuration of the bottom portion is important in facilitating material usage reductions since such configuration can be established to enhance strength characteristics. For example, the bottom portion may be configured to enhance static dome reversal pressure characteristics and to reduce the risk of damage caused when a filled container is dropped onto a hard surface during shipping, storage, and use. This drop resistance may be described as the cumulative drop height (taken from successive drops in which predetermined height increments are added to the previous drop height) at which the bottom portion is damaged sufficiently to preclude the container from standing upright on a flat surface.
As will be appreciated, it is known to reform the bottom portion of a container (e.g., after drawing and ironing processes) in order to define a configuration yielding improved strength characteristics. In this regard, however, known reforming methods and devices have generally presented reliability, repeatability and/or significant production cost drawbacks.